As an example of a control circuit for a load having a phase cut dimmer, consider without limitation a lighting circuit having at least one lamp and being operable with dimmer circuit such as a wall mounted dimmer. It is typically possible to deeply dim the lamp, that is to say to adjust the phase cut dimmer to a low conduction angle. However, when operating the load at low conduction angle, the dimmer is generally very sensitive to mains voltage fluctuations, the reasons for which will be explained in more detail hereinbelow. In particular, a voltage dip may cause the dimmer to switch off, since the phase-cutting device in the dimmer—typically a triac—may not trigger. A deadlock situation can arise, in that the dimmer will not restart, even after the end of the voltage dip; to restart the dimmer, the conduction angle setting is increased significantly, that is to say the user has to turn up the lighting level.
A similar problem can occur when a dimmer is switched on at a very low conduction angle, if the moment of switch-on corresponds to an inappropriate part of the AC phase. Again, the dimmer setting has to be increased to a significantly higher conduction angle before the lamp starts operating.
It would be desirable to avoid, or to reduce, the need to increase the conduction angle necessary to start or restart the lamp.